12.5. Identification of ions and gases
A subsection of Chemistry, 0620, through 12. Experimental techniques and chemical analysis
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The table shows the masses of some ions in a 1000 cm3 sample of toothpaste. name of ion formula of ion mass of ion in 1000 cm3 of toothpaste / g NH4 + 0.2 calcium Ca2+ 1.2 Cl – 0.9 fluoride F– 1.4 magnesium Mg2+ 2.0 phosphate PO4 3– 24.4 sodium Na+ 28.1 sulfate SO4 2– 9.2 tin(Sn2+ 0.2 zinc Zn2+ 0.1 Answer these questions using only the information in the table. State which negative ion has the lowest mass in 1000 cm3 of toothpaste. Name the compound that contains NH4 + and Cl – ions. Calculate the mass of phosphate ions in 250 cm3 of toothpaste.  mass = g Describe a test for sulfate ions. test observations  Toothpaste also contains cinnamal. The structure of cinnamal is shown. C C C H C C C C H H H H H H C C O H Deduce the formula of cinnamal to show the number of atoms of carbon, hydrogen and oxygen. Cinnamal can be oxidised to a carboxylic acid. Draw the structure of a carboxylic acid functional group to show all of the atoms and all of the bonds.  Ethanoic acid is a carboxylic acid. Ethanoic acid reacts like a typical acid. Complete the word equation for the reaction of ethanoic acid with sodium carbonate. ethanoic acid + sodium carbonate sodium ethanoate + +  
0620_s22_qp_31
THEORY
2022
Paper 3, Variant 1
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The table shows the masses of some ions in a 1000 cm3 sample of toothpaste. name of ion formula of ion mass of ion in 1000 cm3 of toothpaste / g ammonium NH4 + 0.5 calcium Ca2+ 3.6 carbonate CO3 2– 2.5 chloride Cl – 0.9 fluoride F– 1.2 Mg2+ 0.2 phosphate PO4 3– 28.0 sodium Na+ 32.0 SO4 2– 10.4 tin(Sn2+ 0.3 Answer these questions using only the information in the table. State which positive ion has the lowest mass in 1000 cm3 of toothpaste. Name the compound that contains Mg2+ and SO4 2– ions. Calculate the mass of sodium ions in 200 cm3 of toothpaste.  mass = g Describe a test for chloride ions. test observations  Toothpaste also contains glycerol. The structure of glycerol is shown. H C H H O H H C O H H C O H Deduce the formula of glycerol to show the number of atoms of carbon, hydrogen and oxygen. Glycerol is an alcohol. Ethanol is also an alcohol. Draw the structure of ethanol to show all of the atoms and all of the bonds.  Name the two products formed when ethanol undergoes complete combustion. and ��������������������������������������������������������������� Give one use of ethanol. 
0620_s22_qp_32
THEORY
2022
Paper 3, Variant 2
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The table shows the masses of some ions in a 1000 cm3 sample of toothpaste. name of ion formula of ion mass of ion in 1000 cm3 of toothpaste / g NH4 + 0.2 calcium Ca2+ 0.8 CO3 2– 0.7 chloride Cl – 0.9 fluoride F– 2.2 magnesium Mg2+ 2.0 phosphate PO4 3– 24.4 sodium Na+ 34.2 sulfate SO4 2– 10.1 tin(Sn2+ 0.4 zinc Zn2+ 0.1 Answer these questions using only the information in the table. State which negative ion has the highest mass in 1000 cm3 of toothpaste. Name the compound that contains NH4 + and CO3 2– ions. Calculate the mass of fluoride ions in 250 cm3 of toothpaste.  mass = g Describe the observations when aqueous ammonia is added drop by drop to a solution containing zinc ions until the ammonia is in excess. observations with a few drops of ammonia observations with ammonia in excess  Toothpaste also contains compound A. The structure of compound A is shown. H C H H H H C O H H C O H Deduce the formula of compoundA to show the number of atoms of carbon, hydrogen and oxygen. CompoundA is an alcohol. EthanoI, C2H5OH, is also an alcohol. Complete these sentences about ethanol using words from the list. different formula group identical molecule similar Ethanol is part of the alcohol homologous series. Each member of the alcohol homologous series has the same functional . Members of the same homologous series have chemical properties that are .  When ethanol undergoes incomplete combustion, a small amount of carbondioxide is produced. Name two other substances that are produced when ethanol undergoes incomplete combustion. and ��������������������������������������������������������������� 
0620_s22_qp_33
THEORY
2022
Paper 3, Variant 3
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This question is about sodium and compounds of sodium. Describe the bonding in a metallic element such as sodium. You may include a diagram as part of your answer. Describe how solid sodium conducts electricity. Some properties of sodium chloride are shown: ● melting point of 801 °C ● non-conductor of electricity when solid ● conductor of electricity when molten ● soluble in water. Name the type of bonding in sodium chloride. Explain why sodium chloride conducts electricity when molten. A student determines the concentration of a solution of dilute sulfuricacid, H2SO4, by titration with aqueous sodiumhydroxide, NaOH. step 1 25.0 cm3 of 0.200 mol / dm3 NaOH is transferred into a conical flask. step 2 Three drops of methyl orange indicator are added to the conical flask. step 3 A burette is filled with H2SO4. step 4 The acid in the burette is added to the conical flask until the indicator changes colour. The volume of acid is recorded. This process is known as titration. step 5 The titration is repeated several times until a suitable number of results is obtained. Name the piece of apparatus used to measure exactly 25.0 cm3 of 0.200 mol / dm3 NaOH in step1. State the colour change of the methyl orange indicator in step4. from to State how the student decides that a suitable number of results have been obtained. 20.0 cm3 of H2SO4 reacts with 25.0 cm3 of 0.200 mol / dm3 NaOH. The equation for the reaction is shown. H2SO4 + 2NaOH → Na2SO4 + 2H2O Calculate the concentration of H2SO4 using the following steps. ● Calculate the number of moles in 25.0 cm3 of 0.200 mol / dm3 NaOH.  mol ● Determine the number of moles of H2SO4 that react with the NaOH.  mol ● Calculate the concentration of H2SO4.  mol / dm3  
0620_s22_qp_41
THEORY
2022
Paper 4, Variant 1
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Calciumhydroxide, Ca(OH)2, is slightly soluble in water. Calciumhydroxide can be made by the reaction of calcium with water. Write the chemical equation for this reaction. Name another substance that reacts with water to form calciumhydroxide. When calciumhydroxide dissolves in water, it dissociates into ions and forms a weakly alkaline solution. Suggest the pH of aqueous calciumhydroxide. Give the formula of the ion responsible for making the solution alkaline. Limewater is a saturated solution of calciumhydroxide, Ca(OH)2. Name the gas limewater is used to test for. Suggest what is meant by the term saturated solution. Describe how you would make a sample of limewater starting with solid calciumhydroxide. Describe how you would test for the presence of calcium ions in a sample of limewater. test observations  A 25.0 cm3 sample of limewater is placed in a conical flask. The concentration of Ca(OH)2 in the limewater is determined by titration with dilute hydrochloricacid, HCl. Name the item of apparatus used to measure the volume of acid in this titration. State the type of reaction which takes place. As well as limewater and dilute hydrochloricacid, state what other type of substance must be added to the conical flask. The equation for the reaction is shown. Ca(OH)2 + 2HCl → CaCl 2 + 2H2O 20.0 cm3 of 0.0500 mol / dm3 HCl reacts with the 25.0 cm3 of Ca(OH)2. Determine the concentration of Ca(OH)2 in g / dm3. Use the following steps. ● Calculate the number of moles in 20.0 cm3 of 0.0500 mol / dm3 HCl.  mol ● Determine the number of moles of Ca(OH)2 in 25.0 cm3 of the limewater.  mol ● Calculate the concentration of Ca(OH)2 in mol / dm3.  mol / dm3 ● Determine the concentration of Ca(OH)2 in g / dm3.  g / dm3  
0620_s22_qp_42
THEORY
2022
Paper 4, Variant 2
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